Small and flat loudspeakers in mobile radio devices and other portable devices typically have a resonance frequency that changes as a function of the temperature and the life of the loudspeaker. In the driving of such loudspeakers, it is possible that the loudspeaker will be permanently damaged if too high a power is provided at this resonance frequency in the driving loudspeaker signal.
Therefore, in the driving of such loudspeakers, many times the total power of the loudspeaker signal is limited, in order to prevent a destruction of the loudspeaker. In this way, however, the efficiency of the driving of the loudspeaker is reduced.
In a different approach for generating a suitable loudspeaker signal, it is attempted to define a transfer function of the loudspeaker with reference to a mathematical model and to derive from the parameters of the loudspeaker model defined in this way a filter function with which frequencies in an input signal to be processed are damped in the region of the resonance frequency. The calculation of the parameters of the loudspeaker model and the derivation of the parameters for the filter function require a computational effort that makes the use of a signal processor necessary. Just in the field of mobile radio devices and portable devices, however, it is desirable to avoid the use of signal processors as much as possible, in order to reduce the energy consumption of the devices and thus to increase the battery operating time.